The present invention discloses an electronic digital device and more particularly relates to electronic digital devices for controlling various vehicles brake or stability systems.
Complex and, in particular, safety-relevant functions of vehicles are increasingly controlled or adjusted by electronic digital devices. Such control or adjusting devices, for example, can be used in connection with the engine of the vehicle, the vehicle brake system, transmission, chassis etc. It is important that these kinds of control systems operate faultlessly so that such modem requirements as environmental friendliness, noise reduction as well as safety requirements can be fulfilled.
Generally, the electronic digital devices mentioned above exhibit an arithmetic unit (CPU), a read-write memory (RAM), a read-only memory (ROM) and more recently also a flash memory (FLS) and interface modules (ITF). These components are used for the internal operations of the electronic digital device as well as for its communication with the sensor means and actuator means.
When the electronic digital device is used in connection with safety-relevant areas, for example brake systems, engine or chassis, it must be ensured that faulty operation is prevented or that it is detected and linked to fail-safe strategies.
In the past, reliable performance of the electronic device was achieved by providing a redundant electronic device. This means that all of the control or adjusting devices are duplicated. The two devices operate on the basis of the same programs and algorithms as well as input values but independently of one another. By means of additional channels and through specially provided data, in particular data based interim results, were exchanged from time to time to determine whether the redundant control or adjusting system obtained the same results. If the results were the same, it was assumed that they were correct. Otherwise an error signal was generated. Although this complete redundancy solves the problem of preventing errors to a certain degree, it has the disadvantage of being extraordinarily expensive, since the same control or adjusting system must be duplicated. Moreover, the process of comparing the data is complicated since it must be ensured that, although the systems work relatively independently of one another, only the data actually corresponding to one another are compared.
DE-A-195 29 434 discloses a microprocessor system for safety-critical control systems. In this system, both a bus and a processor are provided redundantly. The data storage process is not redundant. Although each of these subsystems have a read-write memory and a read-only memory respectively, only the actual data are saved in one system, whereas the corresponding control data, e.g. parity bits, are saved in the other subsystem. When accessing the read-only memory, which is distributed over both subsystems, specialized transmitting devices transmit to the other subsystem those parts that are missing in it. Thus a specialized transmitting device transmits the parity bit from the parity read-only memory to the subsystem to which the parity read-only memory is connected. Also, the data from the data read-only memory are transmitted to the subsystem to which the parity read-only memory is connected via a specialized transmission device. Hence, the data on the two redundant busses are supplemented by a specialized transmitting device respectively and can be used in the same way. When the data of other non-redundant components are to be transmitted from one subsystem to the other, another transmitting device has to be provided which not only transmits the data or test signals but all data prevailing on a bus. Therefore, a complicated system of comparing the data between the two partially redundant systems is required. Furthermore, it has the disadvantage that the saved data themselves are not redundant.
The present invention discloses an electronic digital device for controlling or adjusting processes in a motor vehicle, which allows definite detection of faults and can be manufactured at less cost and in a simpler manner.
In the electronic digital device according to the present invention, hereinafter also referred to as xe2x80x9ccontrol languagexe2x80x9d or xe2x80x9cadjusting systemxe2x80x9d, not all components have to be redundant. The whole system can be partially redundant, with certain components, in particular an arithmetic unit and memory, being redundant and other components not being redundant. Due to a simpler design this reduces the cost and still maintains at least the same safety standard.
In a system that exhibits redundant components, a monitoring device designed as hardware may be provided. This monitoring device compares the data prevailing in the redundant components and generates an error signal if the data deviate from one another. Such a monitoring device may also be used in the partially redundant control or adjusting systems described above.